Abstract Despite progress in providing comprehensive prevention of mother-to-child transmission of HIV (PMTCT) services, significant gaps in the timely uptake and provision of guideline-adherent services and maternal retention in care remain. Such gaps create missed opportunities for preventing mother-to-child transmission and result in nearly 6,100 infants becoming infected with HIV each year in Kenya. Effective interventions that routinize the delivery of evidence- based PMTCT services and foster consistent patient engagement are essential to close the remaining gaps and eliminate mother-to-child transmission of HIV. Building off of a successful R34 grant to develop and pilot test the HITSystem 2.0, an eHealth intervention targeting PMTCT services, the overall goal of this proposal is to use a cluster randomized control design at 12 Kenyan government hospitals to evaluate a modified HITSystem 2.1 intervention. HITSystem 2.1 reflects the 2018 Kenyan PMTCT guidelines, including routine viral load monitoring and interventions to suppress maternal viral load. We aim to evaluate the impact of HITSystem 2.1 to optimize the provision of guideline-adherent services and viral suppression through the antenatal, delivery, and early postpartum periods. Aim 1 of the proposed study will assess the efficacy of the HITSystem 2.1 to increase the proportion of mothers who receive complete PMTCT services (including appointment attendance, medication adherence support, viral load testing, hospital-based delivery, and infant testing per Kenyan National Guidelines) through 6 months postpartum. We hypothesize that mothers receiving the HITSystem 2.1 intervention will have a significantly higher completion rate for guideline-adherence PMTCT services compared to mothers receiving standard of care PMTCT services. In Aim 1b, we will evaluate HITSystem 2.1 implementation using the RE-AIM model to inform sustainable scale up. Aim 2 will assess the efficacy of HITSystem 2.1 to increase viral suppression (<1,000 copies/mL) among pregnant and postpartum women, including those who disengage from care. We hypothesize that mothers at HITSystem 2.1 sites will have higher rates of viral suppression at delivery and 6 months postpartum. Aim 3 will evaluate the cost-effectiveness of the HITSystem 2.1. Driven by differences in PMTCT retention, viral suppression, and modeled estimates of pediatric HIV infections averted, we hypothesize that the HITSystem 2.1 will be cost-effective, based on World Health Organization criteria. This proposal is aimed at improving the quality of PMTCT services in the health facility setting. If efficacious and cost-effective, HITSystem 2.1 holds strong promise for national dissemination.